http://d.puremagic.com/issues/show_bug.cgi?id=5258

           Summary: [CTFE] Stack overflow with struct by ref
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Keywords: rejects-valid
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2010-11-22 17:09:12 PST ---
This D2 program generates a Stack Overflow with DMD 2.050 despite the stack dept is very small:


struct Foo { int x; }
void bar(int n, ref Foo f) {
    if (n)
        bar(n - 1, f);
    else
        f.x++;
}
int spam() {
    bar(1, Foo());
    return 0;
}
enum _ = spam();
void main() {}

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bearophile_hugs@eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |regression


--- Comment #1 from bearophile_hugs@eml.cc 2011-05-06 02:51:16 PDT ---
This CTFE bug is present in DMD v1.068beta still, but it seems absent in DMD v1.042.

A longer example that gives the correct answer with DMD 1.042 but produces stack overflow with DMD v1.068beta:


import std.c.stdio: printf;

bool test(int k, int j, ulong diag45, ulong diag135, ulong cols) {
    return ((cols    & (1UL << j)) +
            (diag135 & (1UL << (j + k))) +
            (diag45  & (1UL << (32 + j - k))) ) == 0;
}

void mark(int k, int j, ref ulong diag45, ref ulong diag135, ref ulong cols) {
    cols    ^= (1UL << j);
    diag135 ^= (1UL << (j + k));
    diag45  ^= (1UL << (32 + j - k));
}

uint solve(int niv, int dx, ref ulong diag45, ref ulong diag135, ref ulong
cols) {
    uint solutions_found;

    if (niv) {
        for (int i = 0; i < dx; i++)
            if (test(niv, i, diag45, diag135, cols)) {
                mark(niv, i, diag45, diag135, cols);
                solutions_found += solve(niv - 1, dx, diag45, diag135, cols);
                mark(niv, i, diag45, diag135, cols);
            }
    } else {
        for (int i = 0; i < dx; i++)
            solutions_found += test(0, i, diag45, diag135, cols);
    }

    return solutions_found;
}

ulong nqueen(int n) {
    // masques
    ulong diag45  = 0; // / diagonal bitboard
    ulong diag135 = 0; // \ diagonal bitboard
    ulong cols    = 0; // column bitboard

    return solve(n - 1, n, diag45, diag135, cols);
}

const ulong result = nqueen(9);

void main() {
    // NQUEENS: 1, 0, 0, 2, 10, 4, 40, 92, 352, 724, 2_680, 14_200, 73_712,
365_596
    printf("%lld\n", result);
}

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--- Comment #2 from Don <clugdbug@yahoo.com.au> 2011-05-06 04:09:57 PDT ---
This is a pseudo-regression: it was never doing what it was supposed to. The test case happened to give the correct results on a previous version, but only because one bug hid another. Slight changes would make it fail.

Ref parameters are not going to work reliably in CTFE until pointers are implemented. Which is not happening in this release.

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--- Comment #3 from Don <clugdbug@yahoo.com.au> 2011-05-17 14:22:02 PDT ---
The bug reported in comment 1 is bug 5845, which is a different bug.

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Don <clugdbug@yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


--- Comment #4 from Don <clugdbug@yahoo.com.au> 2011-05-27 12:52:46 PDT ---
https://github.com/D-Programming-Language/dmd/commit/ff385f5a931b52eea27430ae6d4c6658876f05f0

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Don <clugdbug@yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |verylonglogin.reg@gmail.com


--- Comment #5 from Don <clugdbug@yahoo.com.au> 2011-06-11 22:33:41 PDT ---
*** Issue 6131 has been marked as a duplicate of this issue. ***

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